Stonebraker Corporation has provided the following contribution format income statement. All questions concern situations that are within the relevant range. Sales (9,000 units) $ 270,000 Variable expenses 189,000 Contribution margin 81,000 Fixed expenses 77.400 Net operating income $3,600 Required: a. If sales increase to 9,040 units, what would be the estimated increase in net operating income? b. If the variable cost per unit increases by $6, spending on advertising increases by $3,000, and unit sales increase by 19,200 units, what would be the estimated net operating income? c. Estimate how many units must be sold to achieve a target profit of $26,100